According to Doctor Traolach Brugha, Professor of Psychiatry at the University of Leicester, the research has already revealed that autism was commoner in males, those without higher educational qualifications, and those living in social (government financed) housing. Prevalence was not related to the age of those with the condition.

The findings emerge from the first ever general population survey of autism in adulthood. They are based on a two phase epidemiological survey in England (7,461 screening interviews; 618 diagnostic) carried out in 2007. The findings are now published fully. This means that the survey carried out from Leicester is now internationally endorsed officially.

Brugha said none of the cases with autism found in the community survey throughout England knew that they were autistic or had received an official diagnosis of autism or asperger syndrome.

The new scientific article confirms the already published report from the survey (2009) that 9.8 per thousand adults in England meet official diagnostic criteria for autism spectrum disorder, said Bugha. There was no evidence of an ‘autism epidemic’ of marked increase in people with the condition.

He said: “Overall our findings suggest that prevalence is neither rising nor falling significantly over time. This favours the interpretation that methods of ascertainment (case finding) have changed in more recent surveys of children compared to the earliest surveys in which the rates reported were considerably lower”.

In a comment on the possible causes of autism the researchers suggest that “the - non genetic or environmental - causes of autism appear to be temporally constant, and that recent apparent rises in rates of diagnosis must therefore reflect better case finding, rather than some new environmental toxin. However, we would urge caution and the need for independent replication of this first set of adult community survey findings”.

Brugha also drew attention to the newly reported finding that none of their cases of autism were already known to have the condition: “It is very concerning that none of the cases we confirmed using rigorous diagnostic assessment methods in the community knew that they had the condition or had an official diagnosis. As in all community surveys it is of course likely that most of the cases we found were relatively mild and few were severe. We know that severe autism particularly when accompanied by learning disability is much more likely to be recognised. We are beginning to provide training to psychiatrists in the diagnosis of autism spectrum conditions in adulthood through the Royal College of Psychiatrists Education and Training Centre, London .

The survey was carried out jointly with the National Centre for Social Research (www.natcen.ac.uk) and a team of methodological experts from collaborating Universities (University of Cambridge, UCL, and King’s College, London). The study was supported by the National Health Service Information Centre for Health and Social Care and Department of Health; autism follow-up was supported by the National Institute for Health Research and Department of Health Policy Research Programme.